The light reaching the eye of a human is converted into a bioelectric signal at a photoreceptor and transmitted to the visual cortex. In the case the photoreceptor is damaged, even though other nerve cells are alive, the light is not recognized. Such diseases are representatively retinitis pigmentosa (RP) and age-related macular degeneration (AMD).
A retinal prosthesis system (or a visual prosthesis system) artificially transplants a micro electrode array in a retina cell in order to recover a vision of a disabled person who is visually impaired due to a retina damage, and applies an electric stimulation signal to the transplanted micro electrode array to cause an artificial electric stimulation at the retina cell, so that the electric stimulation signal is transmitted to the cerebrum and allows a person who has lost his sight due to a retina damage to recognize a sight.
The retinal prosthesis system generally includes an image information acquisition device, a signal processing and generating device, and a micro electrode array. The image information acquisition device converts image information into electric signals like an image sensor of a camera, and the signal processing and generating device converts the image signal obtained from the image information acquisition device into an electric stimulation signal for stimulating the retina cell. In addition, the micro electrode array is transplanted in a living body and contacts the retina cell, so that the electric stimulation signal generated by the signal generating device is transmitted to the retina cell to stimulate the retina cell. The micro electrode array may have a two-dimension (2D) structure having a simple planar shape or a sharp three-dimensional (3D) structure which may be embedded deep in the retina organization.
FIG. 1 shows an example of a general retinal prosthesis system. The retinal prosthesis system of FIG. 1 does not include an image sensor.
Referring to FIG. 1, the retinal prosthesis system acquires image information by using an image information acquisition device 101 which is worn by a human body or carried by a human. The image information acquired by the image information acquisition device 101 is transmitted to a signal processor 102, and the signal processor 102 converts the image information into an electric stimulation signal for stimulating the retina cell. The wireless implant 103 receives a signal from the signal processor 102 and transmits the received signal to a micro electrode array contacting the retina cell to stimulate the retina cell.
In the retinal prosthesis system, a device such as a camera is generally worn at a spot on the outside of a human body as the image information acquisition device 101. However, it is cumbersome to wear or carry such a device, and this gives many limitations in free activities of the human. In addition, in order to transmit the image information of an external camera to the micro electrode array transplanted on the eyeball, signals should be connected to the micro electrode array. However, as the micro electrode array has a higher resolution, the number of electrodes connected to the micro electrode array increases exponentially. Therefore, the wiring process is very complicated, and the electrodes should be arranged too densely. For this reason, there is a limit in enhancing the image resolution.
Meanwhile, separate from the image resolution problem, when acquiring image information, a normal person may naturally obtain desired image information by moving the eyeball, for example rotating the eyeball. However, in the general retinal prosthesis system shown in FIG. 1, image information should be acquired not by moving the eyeball but by moving the head or a part of the human body. Therefore, it is impossible to rapidly acquire image information, and the eyeball muscles are degraded since the human does not depend on the movement of the eyeball. This phenomenon is frequently found for persons who are visually impaired, and is called ophthalmodonesis.
FIG. 2 shows another example of a general retinal prosthesis system. The retinal prosthesis system of FIG. 2 includes an image sensor.
Referring to FIG. 2, the retinal prosthesis system may include an image sensor 201, a power source 202 for supplying power and signals, an internal cable 203, an external cable 204 and a plug 205 for electrically connecting the image sensor 201 and the power source 202, or the like. The retinal prosthesis system may acquire image information and stimulate the retina without using an external camera since the image sensor 201 for acquiring images is included therein.
In the retinal prosthesis system, since the image sensor 201 for acquiring image information is transplanted to the eyeball, image information may be acquired by moving the eyeball, without turning the head. Therefore, normal eyeball movement is ensured to eliminate a symptom such as ophthalmodonesis, and natural eyeball movement may be maintained. However, since the retina stimulating system is fabricated depending on a complementary metal-oxide semiconductor (CMOS) process, a 2D micro electrode array with a planar shape may be made, but a micro electrode array with a 3D shape is not easily made. In addition, the retina stimulating system is implemented on a rigid substrate such as a silicon substrate. Therefore, the retina stimulating system is not flexible and thus is not easily adhered and fixed to the eyeball.